Consistent expansion of the demand for data and mixed multimedia information transfer available in a variety of application layer protocols have driven system and network providers to reassess current methods of transport for a wide variety of services which are offered or which can be offered. Higher (application) layer protocols are divided into many group types; for example, asynchronous transfer mode (ATM) protocol data units (PDUS), synchronous transfer mode (STM) PDUs, and variable length (VL) PDUs. VL PDUs can be internet protocol (IP) PDUs, I.E.E.E. 802.3 PDUs, point-to-point protocol (PPP) PDUs, etc. Thus, protocol subtypes exist within each group type as well. Some protocols carry data which is time critical information (e.g.--STM) while other protocols carry delay tolerant information. Current protocols supporting intermediate layers at a transmitter and receiver often are either incapable of handling a variety of application layer protocols, offer limited support of a variety of application layer protocols, or support a variety of application layer protocols but waste extensive amounts of transmission bandwidth as overhead.
For example, transmission of various modes or types of higher layer protocols within ATM packets is one current solution. Packing STM and VL PDUs as ATM cells requires using five bytes of overhead (since all ATM cells have a five byte header) and additional overhead expended with an ATM Adaptation Layer (AAL). Also, additional bandwidth is consumed as overhead in that not every ATM cell is completely filled with data and must be padded to conform to standard ATM length requirements. Much of the overhead is utilized for identifying connections, so end-to-end routing of the ATM cells across routes involving many switches can be carried out. For transmission over a single link, imposition of this overhead is wasteful. Similar waste occurs if internet protocol (IP) is used to carry multiple information types over a single link. Point-to-point (PPP) is another possibility for transmission over a single link. It has somewhat smaller overhead requirements than ATM or IP, but can not support multiple application types, especially those involving stringent delay requirements. Inefficiencies of current protocols are not as detrimental in systems or networks in which bandwidth capacity is underutilized or where the cost of bandwidth is not expensive. However, in systems or networks in which bandwidth capacity is a precious commodity and vigorously competed for, increasing the quantity of bandwidth available for multimedia and data transport and decreasing system transport overhead are valuable, useful, and desirable goals. Therefore, what is needed is a system or network which gracefully transmits various PDU types over a single link while minimizing the overhead demanded in exchange for system flexibility.